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Topic: Reading water reports that state "ppm as CaCO3" (Read 7625 times)

I believe there is some confusion out there, about how to read water reports.Personally, I think I may have been originally mislead by my utility guy to believe that Ca ppm as CaCO3 = Ca ppm.After more research, it appears that:Ca ppm as CaCO3 = (2.5*Ca ppm)Mg ppm as CaCO3 = (4.1*Mg ppm)

wildknight

The molecular weight of CaCO3 is 100.0869 g/ml and the molecular weight of calcium is 40.078 g/mol. For arguments sake, lets round to 100 and 40. So, if your report reads that you have 100 ppm (mg/l) of CaCO3, then you have 40 ppm (mg/l) of elemental calcium in your water. Basically 40% of your CaCO3 reading is elemental calcium.

When you're trying to find the concentration of one substance as another substance you're talking gram equivalent weights.

The equivalent weight of an element can be derived by dividing an element's molar mass by the oxidation number (or, more conveniently, just Google search, "Equivalent weight of x" and you can usually find it. Also, here's a table of equivalent weights: http://www.gewater.com/handbook/control_water_analyses/fig40-2.jsp). In the case of Calcium the equivalent weight is 20.04 (molar mass 40.08 oxidation number 2).

Once you have the equivalent weight of a substance expressing it as ppm as CaCO3 is the easy part. The equivalent weight of CaCO3 is 50 - that's why everything is expressed as CaCO3 - it's easy! It's like a lowest common denominator.